1. Field of the Invention
This invention relates to aeration of liquids and, more particularly, to an improved aeration/mixing apparatus.
2. Description of the Prior Art
Aeration devices are employed in stagnant or polluted bodies of water to promote oxygenation for aquatic life and to assist in the decomposition of pollutants. The principal purpose of the aeration device is to bring air into contact with water over as large an interface as possible in order to promote the rapid transfer of oxygen to the water. In an aeration/mixture system, air is injected through a diffuser under water and allowed to bubble to the surface creating an upwelling current. The transfer of oxygen depends upon bubble size and upon maintaining a constant flow of oxygen-depleted water to the diffuser system. Bubble size depends upon air pressure used to inject air into the liquid and upon the size of the orifice through which the air is allowed to escape. Mathematically it can be shown that the smaller the bubble-for a given rate of air injection--the more area of air to liquid interface exists, thus enhancing the oxygen transfer. A description of various prior art aeration techniques is given in U.S. Pat. No. 4,272,461. As pointed out therein, one of the prior art problems is that gas bubbles, even if small when introduced into the liquid, tend to aggregate into large bubbles as they rise, thus reducing the effective gas-to-liquid interface area.
A further problem with other prior art diffusion-type aerators is that they have been essentially placed in a position of rest on the loose sedimentary material at the bottom of a waterbody. The aeration conducted using such arrangements tends to stir up and resuspend the loose sediments including organic matter which tend to use the oxygen newly dissolved in the water. Nutrients in the bottom sediments are thus re-suspended in the water column defeating the purpose of aeration.
A number of prior art patents have disclosed apparatus to avoid stirring bottom sediment. Typical among these are U.S. Pat. No. 4,107,240 to Verner et al.; U.S. Pat. No. 3,956,432 to Hilling and U.S. Pat. No. 3,799,511 to Svantessoi. Other patents are more directed toward generating turbulent conditions. Illustrative of this latter group are U.S. Pat. No. 4,210,613 to Webb; U.S. Pat. No. 3,679,187 to Smith and U.S. Pat. No. 4,421,696 to Grave et al.